A CONTRIBUTION TO THE ANALYSIS OF HUMAN SPEED OF INFORMATION PROCESSING: DEVELOPMENTAL AND DIFFERENTIAL ARGUMENTS Mislav Stjepan @EBEC Institute of Social Sciences Ivo Pilar, Zagreb UDK: 159.955 Pregledni rad Primljeno: 30. 1. 2004. Speed of human information processing (SIP) is a research construct which has been examined under different names and with different intensity for more than sixty years. Its importance is briefly described in four research fields: differential, experimental, aging and cognitive development. Since SIP presents an important component of contemporary intelligence models and life-span cognitive development research, an attempt for the construction of an integrated SIP picture was necessary. Review and systematic analysis of 42 research papers and additional related literature showed that there are problems with the validity of the SIP construct, but it also revealed other theoretical and empirical inconsistencies. A new proposal for SIP phenomena has been made, which abandons the SIP construct with related measures, and introduces the RCP property as one of the general attributes of every cognitive process. Mislav Stjepan @ebec, Institute of Social Sciences Ivo Pilar, Maruli}ev trg 19/1, p.p. 277, 10001 Zagreb, Croatia. E-mail: [email protected] PROCESSING SPEED AS AN IMPORTANT CONSTRUCT OF HUMAN COGNITIVE FUNCTIONING Speed of information processing (SIP) is probably one of the most intriguing constructs in the research of human intellec- tual functioning. In different times, under different names, it 267 was an object of intensive research in, at least, four psycho- DRU[. ISTRA@. ZAGREB logical research fields: (1) intelligence, (2) experimental cogni- GOD. 13 (2004), BR. 1-2 (69-70), tive psychology, (3) aging and (4) development. STR. 267-292 Intelligence researchers have rather thoroughly analysed @EBEC, M. S.: the speed of human information processing in their attempts A CONTRIBUTION TO... to explain human intellectual abilities. First, at the very begin- ning of scientific psychology (19th century) when Francis Galton tried to prove his eugenic theory of intelligence by using reaction time in addition to other psychological and an- thropometrical measures (Gardner et al., 1999). Later, during the period when psychometric approach dominated the re- search of intelligence, processing speed was considered as an independent factor of non-hierarchical intelligence models (e.g. perceptive speed in Thurstone's Primary Mental Abilities Model) (Gardner et al., 1999), but mostly as a factor of hierar- chical models (e.g. processing speed – second order factor in Horn & Cattell Gf-Gc Theory and in Carroll's Three-Stratum Theory of Cognitive Abilities) (Woodcock, 1994; Bickley et al., 1995). The latest attempt started – and is still under way – with the cognitive correlates approach to intelligence, where pro- cessing speed is one of the key constructs of intelligence mod- els, often labelled as mental speed (Kyllonen, 1994; Neubauer & Knorr, 1998; Roberts et al., 1996; Roberts & Pallier, 2001). On the whole, processing speed has been a clearly recog- nised cognitive ability in intelligence research. Experimental cognitive researchers had the task to pro- pose the most complete theoretical model of human cognitive functioning by analysing the flow of individual information processes during solving some cognitive tasks (starting from initial perception, through a series of other cognitive process- es and resulting in either an observable response or merely in a change of contents of the individual's memory). In that sense, a wide variety of experimental designs and cognitive tasks were designed to isolate the informational flow through different cognitive subsystems (Vernon, 1994; Shepard & Metz- ler, 1971; Sternberg, 1966; Posner & Mitchell, 1967). The time spent in solving cognitive tasks specific to the defined cogni- tive subsystems actually reflects the speed of information pro- cessing in those subsystems. Later on, experimental cognitive research comprising processing speed (or, more precisely, pro- cessing time – the inverse operationalisation of processing speed) started considering the problem of continuity vs. dis- continuity of information processing (Levy and Pashler, 1995; Mulder and van Galen, 1995). Experimental cognitive research also analysed the relationship of processing speed with other aspects of cognitive functioning, (e.g. errors during cognitive task solving) (Nettelbeck, 1994; Coles et al., 1995), and with other constructs important for the description of the human 268 cognitive system – mostly working memory (Hitch et al., 1989; DRU[. ISTRA@. ZAGREB Brandimonte et al., 1992). To summarise, experimental cogni- GOD. 13 (2004), BR. 1-2 (69-70), tive research treated processing speed as a basic property of STR. 267-292 human information processing which served as a key-means @EBEC, M. S.: for examining the components of informational flow through A CONTRIBUTION TO... the human cognitive system and its characteristics (continui- ty, error probability, etc.). Researchers of aging included processing speed quite comprehensively in their attempt at describing the age of re- lated changes in human intellectual functioning. The main reason for that was the role of speed of information process- ing in almost all contemporary models of intelligence and great sensitivity of the processing speed to age related chan- ges. The first research of the influence of age on processing speed described the relationship between the rate of process- ing in young adults and the elderly (Cerella, 1985). Further aging research investigated whether the age related changes of a wide variety of processing speed measures are indepen- dent of each other, or whether they share a significant am- ount of the variance (Salthouse, 2000). Timothy Salthouse sys- tematically investigated the shared variance of age related changes of processing speed and of other cognitive variables, e.g. memory, reasoning, spatial abilities, etc. (Salthouse, 1994a, 1994b, 1998) and tried to define the mediation effect of age related changes of processing speed on age changes of other cognitive variables when they are not assessed in a limited time (Salthouse, 1991, 1994b). Research often focused on the relationship between processing speed and working memory capacity in their mediation of age changes of higher cognitive variables (Salthouse, 1991; Verhaeghen and Salthouse, 1997; Stankov, 1999), and on the examination of the age-complexity relation in adulthood (Salthouse, 1988). Finally, some com- prehensive theoretical models of cognitive slowing in adult- hood were proposed on the basis of processing speed (Myer- son et al., 1990; Salthouse, 1996). Developmental research of processing speed showed that it was the most important, or at least second most impor- tant construct (after working memory capacity) of the infor- mation processing approach to cognitive development. De- velopmental changes of processing speed were recorded very early in developmental psychology through Smith's (1934) research of age changes of simple reaction time on visual sti- muli, and Goodenough's (1935) research of auditory reaction time developmental changes (Wickens, 1974). Systematic re- search of developmental changes in the speed of processing started in the 1970s with the main objective of finding the me- chanism of processing speed development (Wickens, 1974; Chi, 1977; Kail, 1986). The same objective has inspired researchers 269 for the last twenty years and is still on the agenda. The most DRU[. ISTRA@. ZAGREB important question of the research (whose solution implied GOD. 13 (2004), BR. 1-2 (69-70), the answer to the mechanism of processing speed develop- STR. 267-292 ment) was whether the developmental change of processing @EBEC, M. S.: speed is global, or process specific. Precisely, whether the pro- A CONTRIBUTION TO... cessing speed changes during the life-span in the same way for all domains of human cognitive processing or if it changes differently in different domains? If it is global, then the devel- opmental mechanism is mostly (but not completely) deter- mined by neurobiological factors – maturation. If it is process specific, then it is mostly determined by experience – the prac- tice and age changes of different strategies in cognitive task solving. Although process specific explanation has some remarkable evidence (Stiegler et al., 1988; Molenaar & van der Molen, 1994; Ridderinkhof & van der Molen, 1997) there is even more evidence for the global explanation of processing speed development (Hale, 1990; Kail, 1991a, 1991b; Hale et al., 1993; Hale & Jansen, 1994; Kail & Salthouse, 1994; Miller & Vernon, 1997). However, for the purpose of this paper it is re- levant to point out that the neurobiological mechanism (matu- ration) of processing speed development – as a part of global hypotheses – has been verified by some more direct research (Eaton & Ritchot, 1995; Travis, 1998; Rose et al., 2002.). In the last decade, the diversity of developmental studies on pro- cessing speed has been enriched with quite a number of research projects on the developmental relationship between processing speed, working memory and some higher intel- lectual abilities (Kail & Hall, 1994; Kail & Park, 1994; Kail, 1997; Fry & Hale, 2000). Finally, all this specific research of processing speed development and its relationship to other cognitive functions have given arguments to Andreas Demetriou to build one of the most comprehensive theories